The present invention relates to a gas compressor which is used in, for example, a car air-conditioner. More particularly, the invention relates to a gas compressor which is adapted to prevent the occurrence of inconveniences due to oil compression at a time of restarting the operation of the gas compressor, such as an increase in the starting torque.
In a conventional gas compressor, as illustrated in FIG. 18, an open end of a casing 1 is closed by a front head 2 and a main body 3 is disposed within the casing 1. The main body 3 of the compressor has between a front-side block 4 and a rear-side block 5 a cylinder 6 whose inner periphery is substantially elliptical. A rotor 8 is rotatably disposed laterally within a cylinder chamber 7 defined by the blocks 4, 5 and the cylinder 6. The rotor 8 has integrally formed thereon a rotor shaft 8a which passes through end faces of the rotor. The rotor shaft 8a is supported by an F bearing 4a of the front-side block 4 and by an R bearing 5a of the rear-side block 5.
As illustrated in FIG. 19, the rotor 8 has formed therein slit-like vanes grooves 9 in its radial direction. Vanes 10 are mounted in the vane grooves 9 in such a way as to freely advance and retreat. When the rotor 8 rotates, the vanes 10 are urged against the inner wall side of the cylinder 6 by the centrifugal force and the oil pressure at the bottom of the vane grooves.
Small space portions within the cylinder chamber 7 each of which is defined by the front and rear side blocks 4, 5, cylinder 6, rotor 8 and vanes 10 are called "compression chamber space portions 11", each compression chamber space portion having its volume repeatedly varied by the rotation of the rotor 8.
In the above-mentioned main body 3 of the compressor, when the rotor 8 rotates with the result that the volume of each compression space portion 11 varies, the compression chamber space portion sucks a low pressure refrigerant gas from a suction chamber 12 and compresses it due to the variations in the volume.
The high pressure refrigerant gas after having been compressed is discharged into a discharge chamber 16 through discharge ports 13, discharge valves 14, a discharge communication passage 19, an oil separator 15, etc. At this time, the oil separator 15 separates oil from the high pressure refrigerant gas, the thus separated oil being pooled at the bottom of the discharge chamber 16, thereby forming an oil pool 17 in which lubricating oil is pooled.
The lubricating oil in the oil pool 17 is pressure supplied to sliding portions such as the F bearing 4a and the R bearing 5a through an oil passage 18. This pressure supply of the lubricating oil is effected by the high/low pressure difference between the suction chamber 12 or compression chamber 11 and the discharge chamber 16, i.e., the low pressure portion and the high pressure portion.
The lubricating oil that has been supplied to the sliding portions flows finally into the suction chamber 12 that constitutes the low pressure portion and thereafter becomes mist in the low pressure refrigerant gas of the suction chamber 12 and is sucked into the main body 3 of the compressor, wherein the thus sucked oil mist is again compressed together with the refrigerant gas.
However, in the above-mentioned conventional gas compressor, since the forced supply of the lubricating oil to the sliding portions is effected by the high/low pressure difference between the low pressure portion (suction chamber 12 or compression chamber 11) and the high pressure portion (discharge chamber 16), even when the compression operation is stopped, the flow of the lubricating oil from the oil pool 17 to the suction chamber 12 and compression chamber 11 through the oil passage 18 and sliding portions (F bearing 4a, R bearing 5a, etc.) is not stopped so long as the high/low pressure difference exists. Particularly, since after the stoppage of the compression operation no execution is made of the compression/discharge processes, the lubricating oil which has once flown into the compression chamber 11 is not compressed as mist and does not return to the discharge chamber 11 side, with the result that during the stoppage of the compression operation the lubricating oil pools in the suction chamber 12 and compression chamber 11 in large amounts.
When the lubricating oil is pooled in the compression chamber 11 as mentioned above, restarting of the compression operation is accompanied by a so-called "oil compression" wherein the lubricating oil is not compressed as a mist but is compressed as it is in a liquid state, with the result that the starting torque increases and the shock at the starting time of the compression operation also increases.
Furthermore, when the lubricating oil pools in the suction chamber 12, restarting of the compression operation causes the lubricating oil to be sucked into the main body 3 of the compressor not as a mist but in a liquid oil state and compressed. Therefore, in this case also, the oil compression occurs at the time of restarting the compression operation, with the result that the starting torque and the shock at the starting time both increase.